This application is related to co-pending U.S. application Ser. No. 321,227 filed on Nov. 13, 1981, now U.S. Pat. No. 4,446,832, assigned to Nippondenso Co. Ltd.
This invention relates generally to method and system for controlling the idle speed of an internal combustion engine of spark ignition type to suppress the variation in idle engine speed under varying operating conditions.
Various methods and systems for preventing the idle engine speed from undesirably varying in response to rapid load change, and in a conventional method, the intake airflow or air-fuel ratio of the mixture supplied to the engine is controlled for the purpose of controlling idle speed.
In such a conventional method or system, however, a quick response cannot be expected even if the amount of fuel or air-fuel mixture is increased in response to the detection of engine speed drop due to the slow response characteristic inherent to the air supply system and the fuel supply system. Namely, effective torque for compensating for the engine speed drop is generated after the engine speed is lowered to an extent determined by the condition in the absence of various additions, and therefore, such feedback control involving air-fuel ratio control cannot provide desirable quick control of engine idle speed especially in the case of a rapid change. Furthermore an excessive control in such a conventional control results in interference with the feedback control of the air-fuel ratio. As a result of such interference, the effective control would be difficult while there is a fear that extensive hunting for an air-fuel ratio may occur.
In order to solve the above problem caused by the slow response in the air-fuel control system, a control method involving ignition timing control was devised. However, this method also suffers from the problem that undesirable extensive hunting for an engine speed results around a setting speed when the control is peformed excessively.